Method of making patterns for sheet stamping dies



Jan. 24, 1950 w. J. BENTSEN A 5,

METHOD OF MAKING PATTERNS FOR SHEET STAMPING DIES 2 Sheets-Sheet 1 Filed Sept. 17, 1945 INVENTOR. WILLIAM J. BEN TSEN ATTORNEY Jan. 24, 1950 w. J. BENTSEN METHOD OF MAKING PATTERNS FOR SHEET STAMPING DIES 2 Sheets-Sheet 2 Filed Sept. 17, 1945 .NN \NN INVENTOR. WILLIAM J. BENTSEN ATTORNEY Patented ts. 24, 1950 UNITED STATES PATENT OFFICE -METHOD OF MAKING PATTERNS FOR SHEET STAMPING DIES William J. Bentsen, San Diego, Calif., assignor to Solar Aircraft Company, San Diego, Calif., a

corporatlonof California Application September 17, 1945. Serial No. 616,869 3 Claims. (Cl. 22-195) used there has been a pronounced thinning of the metal at and adjacent the shoulder, and an object of the invention is to reduce or eliminate excessive local thinning of the metal.

Another object is to provide a method of producing a thickening of the metal in a die stamping at desired local areas.

Other more specific objects and features of the invention will appear from the detailed description to follow with reference to the drawings.

Briefly, I accomplish the foregoing objects by pre-shaping the metal sheet, prior to placing it between the final dies, in such a way as to provide a bulge in the sheet at. or adjacent the area that would otherwise be excessively thinned during shaping between the final dies. The bulge causes the sheet to have a greater absolute area locally in the region where the final dies would normally stretch and thin the metal excessively. By suitably controlling the extent of the bulge, the thinning of the metal that would otherwise occur can be partially, fully, or over-compensated for. Overcompensation produces an actual thickening of the sheet and is desirable where local reinforcement is advantageous.

The shape and extent of the bulge produced in the preliminary shaping operation must be carefully controlled, else wrinkling of the sheet will be produced in the final dies, and the present invention involves procedures for preparing from the final dies, preliminary dies that will impart the necessary bulge to the sheet. In accordance with one procedure one of the two complementary final dies is altered by superimposing on certain areas thereof a dome of plastic material such as clay, and then using the altered die as a pattern from which to prep e a pair of complementary preliminary dies which the sheet is pre-shaped. After pre-shaping in the preliminary dies, the sheet has a bulge which provides excess area at a local point as compared to the areas of the juxtaposed portions of the final die, so that during final closing movement of the final dies on the sheet the bulge area of the sheet is either stretched to a lesser'extent than it would be if it had not been pre-shaped, or is actually compressed so that its thickness is increased.

In accordance with the second and preferred procedure, the preliminary die. instead of being made directly from the final die as altered by the addition of a dome, is prepared from the altered final die by the procedure covered in the Burger 8: Skinner Patent No. 2,383,706, issued August 28, 1945, and entitled Method of making preliminary shaping die. The procedure described in the Burger 8: Skinner patent involves the making of a preliminary die from a final die by first forming on the surface of the final die a substan- 1 tlally non-compressible and non-stretchable form, removing the form from the final die, fiattening it to a suitable extent without materially altering its absolute area, and then using it as a pattern for the preliminary dies. The procedure in accordance with the present invention diifers from that of the Burger 8: Skinner patent in that the non-compressible and non-stretchable pattern is formed on the original die after the latter has been altered by the addition of the dome, in-

go stead of constructing it directly on the original die.

Referring to the drawing:

Fig. 1 is a perspective view of a plaster pattern for one of a pair of complementary final dies of as such shape as to normally produce excessive thinning of the sheet metal in certain local areas; Fig. 2 is a detailed section taken in the plane II-II of Fig. l, and showing a clay dome built up on a portion of the surface of the plaster pattern of Fig. 1;

Fig. 3 is a section similar to Fig. 2 in all respects except that it is taken in the plane III-HI of Fig. 4 is a detailed cross-section showing a pertion of a pair of complementary dies with a work sheet positioned therebetween, the dies corresponding in shape to the altered pattern of Fig. 3;

Fig. 5 is a section similar to Fig. 3, but showing a reinforced wax pattern formed thereon;

Fig. 6 is a cross-section through the corresponding portion of the reinforced wax pattern shown in Fig. 5 after the pattern has been partially flattened:

Fig. 'l is a detailed cross-section showing a pair of complementary dies with a work sheet therebetween, the dies having been formed from the reinforced wax pattern of Fig. 6;

Figs. 8, 9 and 10 are cross-sections taken in the same plane as Fig. 3, showing successive stages in the shaping, between a pair of complementary ll 6 and 10, but showing the action of the final dies final closing movement of the dies.

3 on a work sheet that has been pre-iormed in dies of the typeshownin Fig. 4: and

Figs. 14, 15 and 16 are views corresponding to Figs. 8, 9 d 10, but showing the action of the final di on a work piece that has been preshaped the preliminary dies of Fig. 7. v

Referring first to Fig. 1, there is shown a pattern 20 for one of a pair of complementary final dies to be used in shaping sheet metal. The

pattern 20 corresponds exactly in shape to the final die actually used to shape the metal, the only difference being that whereas the final die would usually be made of some metal or alloy, the pattern 20 is usually made of some material such as plaster that better lends itself to manufacture. It will be observed that the pattern 2' is of a die intended for the shaping of sheet metal into a rather irregular shape involving a relatively high fiat portion 2| (Fig. 3) bounded by a shoulder 22 beyond which the surface falls away in relatively steep sides 22. The particular shape shown also involves a break 24 which joins the fiatportion 2'l to a second flat portion 25 at a slightly lower level.

Referring now to Figs. 8, 9 and 10, there are shown portions of the final dies 20 and 32 corresponding to the portions of the plaster pattern 20 shown in Fig. 3, the final die 30 being identical in configuration with the plaster pattern 20. Figs. 8, 9 and 10 show the action of the dies on an originally fiat work sheet 21 as it is pressed or stamped between the dies 20 and 32 during It will be observed that in Fig. 8 the work piece has been caught on the shoulder 22 of the die 30 and is frictionally engaged by the upper die 32 at points 28 and 29 spaced outwardly and below the shoulder 22, and that the sheet metal is being thinned immediately below the shoulder 22. In Fig. 9 this thinning has increased as the dies move closer together. In Fig. 10 the dies are in their final positions in which the spacing therebetween corresponds to the original thickness of the work sheet 21. However, it will be observed that because of the stretching of the work sheet adjacent the shoulder 22 of the die 30, it fails to fill the space between the dies. The thirming produced in actual operation is not as great as has been indicated in Figs. 8, 9 and 10, because the thinning has been exaggerated in the drawing to explain the action. However, the thinning is frequently so great as to dangerously weaken the work piece, particularly where it constitutes a part, such as the part ,of a stainless steel exhaust manifold, which is exposed to corrosive gases at high temperature, in service. I have discovered that the thinning of the work sheet described with reference to Figs. 8, 9 and 10, can be greatly reduced or eliminated by suitably pre-shaping the work piece before it is placed between the final dies. This pre-shaping is performed in accordance with the invention in preliminary dies the patterns for which are constructed from one of the final dies or a counterpart plaster pattern such as that illustrated in Fig. 1. v

The first step in preparing the pattern for the preliminary dies in accordance with the invention, is to form over the high relatively fiat portions 2|, 24 and 25 of the pattern 20, a dome 34 of the general shape illustrated in Figs. 2 and 3. The dome can be formed of any suitable plastic material, such as clay, and is suitably rounded so that it increases gradually in thickness in wardly from the shoulder 22. the exact thickness 4 and shape of the dome being determined by experiment, since no fixed rule can be established that will apply to all of the innumerable shapes into which sheet metal may be die-stamped. In accordance with the first procedure previously mentioned, the altered plaster pattern 20 of Figs. 2 and 3 itself constitutes a pattern ,to form a die 21 (Fig. 4) of identical shape, and from this die 31 a complementary die is is formed in accordance with standard procedures. A fiat work piece 39 is then shaped between the dies 21 and 38 by pressing or stamping in accordance with standard procedures, and the preformed sheet 39 is then finished between the final dies 30 and 32, the action of the pre-formed sheet during the final closing movement of the dies being illustrated in Figs. 11, 12 and 13.

It will be observed that whereas the sheet 21 in Fig. 8 is substantially fiat across the top of the lower die 20 and is being stretched below the shoulder 22 of the die, the sheet-39 in Fig. 11 has a pronounced bulge between the flat portions of,the upper and lower dies and hugs the lower die 30 at the sides so that there is no stretching of the sheet comparable to that which occurs in Figs. 8, 9 and 10. Furthermore, in Fig. 11 the length of the bulged portion of the sheet between the shoulders 22 is greater than its finished length as shown in Fig. 13, so that this portion of the sheet is actually compressed. instead of being stretched during the final movement between the dies 20 and 32.

However, it will be observed from inspection of Fig. 13, that while the thinning of the metal sheet 29 is much less than that of the sheet 21 in Fig. 10, it is thinned slightly below the normal thickness of the sheet, which is equal to the spacing between the dies in Fig. 13. This thinning, however, resulted during the preliminary shaping operation between the dies 31 and 38 (Fig. 4) because of the deep draw that was made between those dies. This thinning of the work sheet during the preliminary stamping operation can be prevented in accordance with the second procedure referred to hereinabove, which will now be described with reference to Figs. 5, 6 and 'I.

In Fig. 5, the modified original plaster pattern 20 of Figs. 2 and 3 has been used to form a flexible but substantially non-stretchable sheet pat- 50 tern 40 which may be composed of wax reinforced with a fabric such as cheesecloth.

The sheet pattern 40 can be built up on the domed plaster pattern 20 of Figs. 2 and 3 by first coating the surface of the domed pattern 20 with 55 a layer of melted wax 4|, and while this wax is still soft, pressing into it a reinforcing layer of cheesecloth 42. The cheesecloth is relatively flexible and can be readily shaped to correspond with the surface of the domed pattern 20. Thereafter,

m a second layer of wax 43 is brushed onto the cheesecloth 42, after which a second layer 44 of cheesecloth is pressed into the wax. The cheesecloth layer 44 is laid with its threads extending diagonally with respect to the threads of the first g5 cloth layer 42, so that the resultant sheet pattern 49 is reinforced against stretching in any direction. A final coating 45 of wax can then be brushed onto the cheesecloth layer 44.

After the sheet pattern 40 has cooled and solidi- 7 fled, it is lifted 011 of the domed pattern 20 and itsdepth reduced by bending and flexing, but with very little stretching, so that the projected area of the sheet pattern is substantially increased, as shown in Fig. 6, without materially increasing 75 its absolute area. The sheet pattern 40 is then used as a pattern from which to construct a die 41 (Fig. 7) of corresponding shape by conventional molding and casting procedures. For more specific information as to an actual process that may follow in producing the sheet pattern 40, and producingthe die 41 from the sheet pattern 40, reference 15 made to the aforementioned Burger & Skinner Patent No. 2,383,706.

After the die 47 has been constructed, a complementar die 48 is made from it by conventional methods. The dies 41 and 48 constitute the preliminary dies for shaping a work sheet 50 prior to its being placed between the final dies 30 and 32 (Figs. 14, 15, and 16).

By virtue of the fact that the dies 41 and 48 made from the domed pattern 20 by the described process employing the sheet pattern 40, is of substantially reduced depth, there is much less thinning of the work sheet 50 during preliminary shaping thereof between the dies 41 and 48, than results during the preliminary shaping of the work sheet 39 between the preliminary dies 31 and 38 (Fig. 4). This is because a sheet shaped between relatively shallow complementary dies has an opportunity to draw inwardly from the edges and acquire the desired shape with relatively little stretching (and consequent thinning) of the metal as compared to the stretching resulting from the pressing of the same sheet initially between deeper dies. However, the work sheet 50 is provided with the required bulge and resultant increased local area, so that when it is shaped between the final dies, excessive thinning of the material is prevented.

Thus, as shown in Fig. 14, the work sheet 50 is bulged between the shoulders 22 of the die 38 substantially the same as the work sheet 39 is bulged in Fig. 11. However, the sheet 50 is initially not thinned by the preliminary shaping operation to the extent that the sheet 39 was. Hence, during final movement of the dies 30 and 32 as shown in Figs. 15 and 16, the work piece 50 retains its original thickness and substantially.

completely fills the space between the dies 30 and 32.

As illustrated in Fig. 16, the sheet 50 has been given just sufiicient local bulge in the region of the high part of the die 30, so that it preserves substantially its original thickness after the final stamping operation. However, by increasing the height of the dome 34 (Figs. 2 and 3) a greater bulge can be imparted to the sheet to increase its area in the region juxtaposed to the high flat area of the final dies and cause lateral compression of the metal to actually increase the thickness. It may be desirable in some instances to provide increased thickness at local areas exposed to extra strain, or to extra high temperatures. It will be observed that in Fig. 16 the sheet 50 has been forced well into the corners 52 and 53 of the upper die 32, actually increasing the thickness of the sheet along the shoulder thereof.

Although for the purpose of explaining the invention it has been described with reference to a specific shape presenting the problem to be solved, obviously, the method is applicable to a wide variety of shapes involving steep sides and relatively sharp shoulders or corners, and the invention is to be limited only to the extent set forth in the appended claims.

I claim:

1. In the art of die stamping and drawing sheet metal between complementary final dies the surface of one of which has a high relatively flat portion bounded by ashoulder beyond which the surface slopes steeply, the method of preparing a pattern for a preliminary die for pre-shaping a sheet to reduce thinning thereof adjacent said shoulder during shaping in said final dies, which method comprises: building up said relatively flat portion of said one final die into a rounded dome, the edge of which merges into said shoulder; forming on said domed die a flexible substantially non-stretchable sheet pattern; removing said sheet pattern from said domed die and partially flattening it to reduce its depth and increase its projected area without materially changing its absolute area; said flattened sheet pattern constituting the desired pattern.

2. In the art of die stamping and drawing sheet metal between complementary final dies the surface of one of which final dies has a-steeply sloping portion adjacent a flatter portion, the method of preparing a pattern for a preliminary die for pre-shaping a sheet to reduce thinning thereof adjacent the juncture of said portions during shaping in said final dies, which. method comprises: building up said flatter portion of said one final die into a dome; forming on said domed die a flexible, substantially non-stretchable sheet pattern; removing said sheet pattern from said domed die and partially flattening it to reduce its depth and increase its projected area without materially changing its absolute area; said flattened sheet pattern constituting the desired pat tern.

3. The method of preparing a pattern for a preliminary die for pre-shaping a sheet to reduce thinning thereof during shaping in a final die having a high relatively flat portion bounded by a shoulder beyond which the surface slopes steeply, which method comprises building up said relatively flat portion of said final die into a rounded dome the edge of which merges into said shoulder and forming on said domed die a flexible substantially non-stretchable sheet pattern, removing said sheet pattern from said domed die and partially flattening it to reduce its depth and increase its projected area without materially changing its absolute area, and using said flattened sheet pattern as a pattern to form the desired die.

WILLIAM J. BENTSEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 189,729 Habermehl Apr. 17, 1877 808,177 Thiem Dec. 26, 1905 1,982,318 Oestnaes Nov. 27, 1934 2,120,987 Murray June 21, 1938 2,261,181 Rempel Nov. 4, 1941 2,274,060 Hart Feb. 24, 1942 2,280,864 Stossel Apr. 28, 1942 2,383,706 Burger Aug. 28, 1945 FOREIGN PATENTS Number Country Date 557,288 Great Britain Nov. 15, 1943 

